Arthropods Flashcards
(36 cards)
Approximately how many species are there of beetles, insects, and terrestrial arthropods?
About 1.5 million beetles, 5.5 million insects, and 7 million terrestrial arthropods.
How many crustacean species are known, and where do most live?
Over 50,000 species, mostly aquatic.
What percentage of all animals are arthropods?
75%-80%.
What type of symmetry and embryonic development do arthropods have?
Bilateral symmetry, triploblastic protostomes.
What are the characteristics of arthropod body segments?
Each segment has paired, segmented, jointed appendages, some evolved into mouthparts.
What is tagmatisation (tagmosis) in arthropods?
Division of the body into functional groups of segments called tagmata, typically head and trunk (thorax and abdomen).
What are the main sclerites in an arthropod body segment?
Dorsal tergum, ventral sternum, and lateral flexible pleuron.
What is the arthropod body cavity called, and what does it contain?
Open haemocoel; organs bathed in haemocoelic fluid (blood).
What layers make up the arthropod cuticle?
Epicuticle (outer) and procuticle (inner), with procuticle subdivided into exocuticle and endocuticle.
How are arthropod limbs jointed?
By articular membranes—thin flexible cuticle joining sclerites at articulation points.
What are condyles in arthropods?
Contact or bearing points between sclerites.
Why can’t arthropods grow gradually?
Their rigid exoskeleton must be shed during moulting (ecdysis).
What hormone controls moulting?
Ecdysone.
What are intermoult stages called?
Instars.
What happens during moulting?
Enzymes digest old endocuticle, new soft cuticle secreted beneath, old cuticle splits, body swells, new cuticle hardens by sclerotization.
What is the difference between uniramous and biramous limbs?
Uniramous: single branch (endopod), usually for walking; biramous: two branches (endopod and exopod), often for swimming.
What adaptations do arthropods have for gas exchange?
Specialized respiratory systems with high surface area to volume ratios.
What excretory organs do arthropods have?
Nephridia (take waste from coelom), Malpighian tubules (attached to stomach, in body cavity).
What types of eyes do arthropods have?
Compound eyes and ocelli (simple eyes).
How is the arthropod exoskeleton hardened?
By sclerotization (tanning), cross-linking protein molecules.
How is exoskeleton hardening different in crustaceans?
Further hardened by mineralisation—calcium carbonate deposits in procuticle.
What are benefits of the exoskeleton?
Strong protection from predators and water loss.
What are drawbacks of the exoskeleton?
Restricts growth (needs moulting), relatively heavy (limits land locomotion), and limits respiration/excretion unless thin
How have arthropods compensated for sensory limitations caused by the exoskeleton?
Developed new sensory structures to sense the external environment.
